What happened here?

[Nedum]

So I was pushing the limits and at the end of this track I've done something that only can be happen with a super sport aerobatic AC, a over Nose negativ flip @ 380 kph. I know that military ACs can do much more things than a Cessna but a negativ flip Su27 negativ flip.trk I can hardly believe. :music_whistling:

Watch and get big eyes! :D

 

€dit: @ a Mod please change the heppened to happened at the thread title

Edited February 22, 2015 by Nedum

[EngineerFalcon]

Can't see your track right now, but I assume you mean inverted departure right ? It can happen easily if you're not careful, and as far as I know it is not unrealistic by any means - The Flanker was designed aerodynamically unstable and the FCS can't always hold her in place.

[Nedum]

You must see the track.

I was doing a half loop with 180° roll, but to near at the ground.

I managed to raise the nose @480 kph/full AB. Suddenly the nose raises up alone @420kph. I give a short but hard push to the stick so the nose moves at level @390 kpH, but then the whole plane makes a 90° flip forward @380kph.

Like a rocket without any wing. The whole time the AB was at full power.

At some moments the DCS Su27 behaves like a rocket without any wing, there is no air drag where it should be and there is air driag where it shouldn't.

It looks like the DCS Su27 is hanging at some ropes and swings around like a marshal arts artist. It's like in some movies where you can see that's not natural, because the move fits not to the rest of the movements.

Even a modern acrobatic plane moves of a more natural way. Speed, the lost of speed and therefor the ballistic movemnt fits, but that all is still missing in DCS for the Su27. She is doing things, even she could do this things, that are looking and feeling plain wrong!

 

So please look the track!

Edited February 24, 2015 by Nedum

[Ironhand]

Had time this morning to watch your track a few times. First, I enjoyed watching you fly the routine. My only comment is that, on that last loop, when you came over the top with such limited airspeed and a low altitude, you should have abandoned the routine and recovered the aircraft. I read the numbers on the HUD and thought: Uh-oh. :)

 

Anyway, I think what happened was that, as you pulled out and pushed the stick full forward, you didn't anticipate the aircraft and pull the stick back quickly enough. You got that nose down momentum going and didn't have the airspeed to overcome it.

 

I'm not sure how you were trimmed during that part of the flight but it almost looked like there was no trimming. What I found interesting, however, is that there were times when you were pulling back on the stick but your horizontal stabilizer was actually in a pitch down position. Slow down the sim to 1/4 speed (so you'll have plenty of time to watch things unfold) and switch back and forth between the cockpit and F2 views and you'll see what I mean. Mechanically, you were pulling back on the stick but the FBW system was reinterpreting it.

 

Don't have more time to investigate further. Wish I did. But take a look at it for yourself at a slower speed. What remains, regardless, is that, once the nose down momentum was started, you were late recovering. It might be worth taking control in those final seconds and see if you can recover by reacting more quickly to what you're setting in motion.

 

But, again, I enjoyed watching your flight immensely...right up until that final loop.

[Yo-Yo]

Had time this morning to watch your track a few times. First, I enjoyed watching you fly the routine. My only comment is that, on that last loop, when you came over the top with such limited airspeed and a low altitude, you should have abandoned the routine and recovered the aircraft. I read the numbers on the HUD and thought: Uh-oh. :)

 

Anyway, I think what happened was that, as you pulled out and pushed the stick full forward, you didn't anticipate the aircraft and pull the stick back quickly enough. You got that nose down momentum going and didn't have the airspeed to overcome it.

 

I'm not sure how you were trimmed during that part of the flight but it almost looked like there was no trimming. What I found interesting, however, is that there were times when you were pulling back on the stick but your horizontal stabilizer was actually in a pitch down position. Slow down the sim to 1/4 speed (so you'll have plenty of time to watch things unfold) and switch back and forth between the cockpit and F2 views and you'll see what I mean. Mechanically, you were pulling back on the stick but the FBW system was reinterpreting it.

 

Don't have more time to investigate further. Wish I did. But take a look at it for yourself at a slower speed. What remains, regardless, is that, once the nose down momentum was started, you were late recovering. It might be worth taking control in those final seconds and see if you can recover by reacting more quickly to what you're setting in motion.

 

But, again, I enjoyed watching your flight immensely...right up until that final loop.

 

As you found time to look at this track, could you say whether -0.5 g limit for IAS less than 300 kph was overcome? If so - the plane was pulled into prohibited area.

 

The manual prescribes to perform unloaded flight in the situation of loosing speed in nose-up attitude.

[Ironhand]

As you found time to look at this track, could you say whether -0.5 g limit for IAS less than 300 kph was overcome? If so - the plane was pulled into prohibited area.

 

The manual prescribes to perform unloaded flight in the situation of loosing speed in nose-up attitude.

His IAS was around 380k/hr at the time. And he did negative-G the aircraft. My impression was that he didn't anticipate the aircraft. He waited until the nose was actively dropping before neutralizing the force. By the time he reacted he was well into negative-G territory and nothing was going to stop what happened next.

 

Again, that's just my impression. I saw the stick push forward and expected to see it immediately come back. But it didn't. If it had, I think he would have saved it.

[Yo-Yo]

His IAS was around 380k/hr at the time. And he did negative-G the aircraft. My impression was that he didn't anticipate the aircraft. He waited until the nose was actively dropping before neutralizing the force. By the time he reacted he was well into negative-G territory and nothing was going to stop what happened next.

 

Again, that's just my impression. I saw the stick push forward and expected to see it immediately come back. But it didn't. If it had, I think he would have saved it.

 

Ok, but I can suggest that the plane decelerated very quickly to 300 and further. Anyway, hard and fast pulling is no that is directed in the manual... :)

 

By the way, there is an opportunity to take control in the track just before this pulling and try to escape this situation.

[Ironhand]

...

 

By the way, there is an opportunity to take control in the track just before this pulling and try to escape this situation.

Just did that. Recovered without a problem.

Edited February 25, 2015 by Ironhand

[Nedum]

Had time this morning to watch your track a few times. First, I enjoyed watching you fly the routine. My only comment is that, on that last loop, when you came over the top with such limited airspeed and a low altitude, you should have abandoned the routine and recovered the aircraft. I read the numbers on the HUD and thought: Uh-oh. :)

 

Anyway, I think what happened was that, as you pulled out and pushed the stick full forward, you didn't anticipate the aircraft and pull the stick back quickly enough. You got that nose down momentum going and didn't have the airspeed to overcome it.

 

I'm not sure how you were trimmed during that part of the flight but it almost looked like there was no trimming. What I found interesting, however, is that there were times when you were pulling back on the stick but your horizontal stabilizer was actually in a pitch down position. Slow down the sim to 1/4 speed (so you'll have plenty of time to watch things unfold) and switch back and forth between the cockpit and F2 views and you'll see what I mean. Mechanically, you were pulling back on the stick but the FBW system was reinterpreting it.

 

Don't have more time to investigate further. Wish I did. But take a look at it for yourself at a slower speed. What remains, regardless, is that, once the nose down momentum was started, you were late recovering. It might be worth taking control in those final seconds and see if you can recover by reacting more quickly to what you're setting in motion.

 

But, again, I enjoyed watching your flight immensely...right up until that final loop.

 

Thanks for watching.

Yes you can recover the AC, but that is not the problem.

The way the DCS Su27 get in this 2 situations are the more interesting things.

If I know what will happened next, I fly simply very different and so I can recover.

The lowest speed in this track is a way over such a flip behavior. And I am wondering where are all this forces comming from and going to, to do such an maneuver? And where is the air drag coming from to lift suddenly the nose and why is suddenly the air drag gone with only a lost of 20 kph (400kph -> 380 kph) and full ab and the nose at level? It feels like there are no wings in this moments.

At both moments the AC handles like it was stalling and even with nose at level, full AB and 380 kph, the AC keeps stalling! Like there is all air drag gone.

And as I said above... I can fley all this and much more maneuvers blindfold.. but that's not the problem. If you want, you can dance with raw eggs on your shoulders or fly the DCS Su27, but I want to push the limits and the DCS Su27 limits coming to soon, to suddenly and to hard.

I now try to do a whole 360° flip, and I think I will get this "miracle" at weekend. Till now I can do a 230° flip but we will see.. may I'll be lucky next time... it's a thing about power timing and stick timing. But I can't believe you can do such things with the real Su27.

[Ironhand]

Thanks for watching.

Yes you can recover the AC, but that is not the problem.

The way the DCS Su27 get in this 2 situations are the more interesting things.

If I know what will happened next, I fly simply very different and so I can recover.

The lowest speed in this track is a way over such a flip behavior. And I am wondering where are all this forces comming from and going to, to do such an maneuver? And where is the air drag coming from to lift suddenly the nose and why is suddenly the air drag gone with only a lost of 20 kph (400kph -> 380 kph) and full ab and the nose at level? It feels like there are no wings in this moments.

At both moments the AC handles like it was stalling and even with nose at level, full AB and 380 kph, the AC keeps stalling! Like there is all air drag gone.

And as I said above... I can fley all this and much more maneuvers blindfold.. but that's not the problem. If you want, you can dance with raw eggs on your shoulders or fly the DCS Su27, but I want to push the limits and the DCS Su27 limits coming to soon, to suddenly and to hard.

I now try to do a whole 360° flip, and I think I will get this "miracle" at weekend. Till now I can do a 230° flip but we will see.. may I'll be lucky next time... it's a thing about power timing and stick timing. But I can't believe you can do such things with the real Su27.

I'll have time this weekend (hopefully) to take another look at the original track. But as far as stalling is concerned, nose level and 380 k/hr does not mean that you aren't stalling the wing. The issue, as always, is the AoA of the wing--the direction the air is hitting it. And that's determined by the direction in which your aircraft is actually moving through the air. But you know that. So I hope to have time to take a closer look. I do know that it can take Nadia awhile to recognize what I can already feel through the aircraft--that I'm flying again. And all the while she's still screaming at me. :)

 

If you make the full 360, that'll be something. In a way, though, I hope you don't succeed, if you understand what I mean. :)